Failed to load plugin resource as stream {} with classLoader

Error message

Failed to load plugin resource as stream {} with classLoader {}

What it means

PluginClassInjector.getResourceAsStream fetches a plugin class's bytecode stream via the URL or plain handler. Any Throwable during routing or lookup is logged with this warn and null is returned; the error is deliberately swallowed so instrumentation can degrade instead of crashing. Null means the resource stream is unavailable.

Source

Thrown at agent-module/profiler/src/main/java/com/navercorp/pinpoint/profiler/instrument/classloading/PluginClassInjector.java:99

        }
    }

    @Override
    public InputStream getResourceAsStream(ClassLoader targetClassLoader, String internalName) {
        try {
            if (bootstrapCore.isBootstrapPackageByInternalName(internalName)) {
                return bootstrapCore.openStream(internalName);
            }
            if (targetClassLoader == null) {
                return bootstrapClassLoaderHandler.getResourceAsStream(null, internalName);
            } else if (targetClassLoader instanceof URLClassLoader) {
                final URLClassLoader urlClassLoader = (URLClassLoader) targetClassLoader;
                return urlClassLoaderHandler.getResourceAsStream(urlClassLoader, internalName);
            } else {
                return plainClassLoaderHandler.getResourceAsStream(targetClassLoader, internalName);
            }
        } catch (Throwable e) {
             logger.warn("Failed to load plugin resource as stream {} with classLoader {}", internalName, targetClassLoader, e);
            return null;
        }
    }
}

View on GitHub (pinned to 744c3d3075)

Solutions

Check the exception stack trace attached to this warn for the true cause.
Fix loader routing so only URLClassLoaders reach urlClassLoaderHandler.
Validate internalName (package/path + ".class") and that the resource exists in the plugin jar.
Ensure call sites null-check the returned stream before reading.

Example fix

// before
byte[] bytes = IOUtils.toByteArray(injector.getResourceAsStream(targetClassLoader, internalName));
// after
InputStream in = injector.getResourceAsStream(targetClassLoader, internalName);
if (in == null) { return null; }
byte[] bytes = IOUtils.toByteArray(in);

Defensive patterns

Strategy: fallback

Validate before calling

if (targetClassLoader instanceof URLClassLoader) { /* url handler path */ } else { /* plain handler path */ }

Type guard

static InputStream safeGetResource(PluginClassInjector injector, ClassLoader cl, String internalName) {
    InputStream in = injector.getResourceAsStream(cl, internalName);
    return in != null ? in : cl.getResourceAsStream(internalName);
}

Try / catch

InputStream in = injector.getResourceAsStream(cl, internalName);
if (in == null) { log.warn("resource {} unavailable", internalName); return null; }

Prevention

Null-check the stream before reading
Only route URLClassLoaders to the URL handler
Use correct internalName format (path/Foo.class)
Avoid lookups on closed/redeployed classloaders

When it happens

Trigger: Any Throwable thrown by urlClassLoaderHandler.getResourceAsStream (e.g. ClassCastException when the loader is not a URLClassLoader) or plainClassLoaderHandler.getResourceAsStream while resolving internalName.

Common situations: Non-URLClassLoader loaders incorrectly routed to the URL handler; closed webapp classloaders after redeploy; unreadable plugin jar; wrong internalName format.

Understand the failure class

Background: 'Could not be found', 'does not exist', 'not found in database': the resource-not-found family when an ID, slug, key, or URI lookup comes back empty — this error's family across 20 libraries.

Related errors

AI-assisted analysis of pinpoint-apm/pinpoint@744c3d3075 (2026-09-07). Data as JSON: /api/errors/be900c3a9d7c38a3. Report an issue: GitHub.